Electrophotographic photosensitive members using an inorganic photoconductive material such as selenium, a selenium alloy, zinc oxide, cadmium sulfide, etc., have been mainly used in the past. However, the electrophotoconductive photosensitive members using inorganic photoconductive materials have problems in the points of producibility, production cost, flexibility, etc.
Recently, for solving such problems, organic photoconductive materials have been vigorously pursued; and electrophotographic photosensitive members using a charge-transfer complex composed of polyvinyl carbazole and 2,4,7-trinitrofluorenone and electrophotographic photosensitive members using an eutectic complex of a pyryrium salt and alkylidenediarylene are known.
Also, most recently, an electrophotographic photosensitive member wherein a function of generating a charge by absorbing light and a function of transporting the charge thus generated are allocated to separate materials is proposed. For example, a double layer or multilayer type electrophotographic photoconductive member separately containing a bisazo pigment and a pyrazoline derivative in these layers in proposed as described in JP-A-58-16247 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Furthermore, recently, it is proposed to prevent the increase of a residual potential by incorporating a cyanovinyl compound in a charge transporting layer together with an electron donative charge transfer material as described in JP-A-58-7643.
However, the electrophotographic photosensitive members using these organic photoconductive materials have low photosensitivity and are yet insufficient as photosensitive members. Also, the double layer or multilayer type electrophotographic photosensitive member wherein functions are allocated to a charge generating layer and a charge transporting layer having sufficiently satisfactory characteristics for practical use has not yet been obtained.
That is, in the double layer type electrophotographic photosensitive member having a charge generating layer and a charge transporting layer successively formed on a support, the photosensitivity is insufficient; and there are problems that the photosensitivity and the charging potential are largely changed by changes in the environmental conditions and also the potential cycle changes in the light-exposed portions whenever unexposed portions are large.
These problems are also seen in an ordinary process of transferring toner images formed by tonerdeveloping non-exposed portions on a photosensitive member onto a transfer material such as a paper but are particularly remarkable in an image-forming process including the steps of uniformly negatively charging a photosensitive member, forming electrostatic latent images by exposing the member to image-bearing radiation, forming toner images by development, and applying thereto a positive charge at the transfer of the toner images. That is, since the potentials at the exposed portions and the unexposed portions of the aforesaid photosensitive member greatly changes during a cycle, the density of the transferred images greatly differs between the initial images and images after making many copies. Also, when after making many copies, transfer papers are changed into transfer papers having a large size, the transfer density at the portions of the large transfer paper corresponding to the widened portions becomes higher or fog is formed at the portions.